Probing Kalb-Ramond gravity with charged rotating black holes: constraints from EHT observations
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| Format: | Preprint |
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2026
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| _version_ | 1866915938003058688 |
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| author | Nengroo, Towheed Ahmad Islam, Shafqat Ul Ghosh, Sushant G. |
| author_facet | Nengroo, Towheed Ahmad Islam, Shafqat Ul Ghosh, Sushant G. |
| contents | The Event Horizon Telescope (EHT) has guided strong-field gravitational physics by providing the first direct images of the supermassive black holes M87* and Sagittarius A*. The EHT observations offer unprecedented opportunities to test modified gravity theories against general relativity (GR). Motivated by this, we investigate charged rotating black holes in KR gravity, a framework motivated by string theory that incorporates spontaneous Lorentz symmetry breaking. The spacetime geometry is characterized by a Lorentz--violating parameter $\ell$ and electric charge $Q$, which modify the Kerr--Newman metric through a radial-dependent mass function. We compute black hole shadows and derive constraints on $\ell$ and $Q$ using EHT observations of M87* and Sgr A*. For angular shadow diameter $θ_{\rm sh}$ of M87* at inclination $θ_o=17^\circ$ and fixed $Q=0.2$, the EHT-allowed range $θ_{\rm sh}\in(35.1,\,40.5)\,μ\mathrm{as}$ constrains the Lorentz--violating parameter to approximately $-0.019\lesssim\ell\lesssim0.075$ and $-0.076\lesssim\ell\lesssim0.029$ across the admissible spin interval. For angular shadow diameter $θ_{\rm sh}$ of Sgr A* at inclination $θ_o=50^\circ$ and fixed $Q=0.2$, the corresponding EHT-allowed range $θ_{\rm sh}\in(41.7,\,55.7)\,μ\mathrm{as}$ permits approximately $-0.075\lesssim\ell\lesssim0.110$ and $-0.124\lesssim\ell\lesssim0.076$ across the admissible spin interval. Our analysis reveals that the Lorentz-violating parameter suppresses the shadow radius by a factor $\sqrt{1-\ell}$, while charge introduces additional distortions. Using the angular shadow diameter measured by EHT, we obtain an upper bound $\ell \lesssim 0.19$ from Sgr A* data with the stellar dynamics mass prior. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2604_13494 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Probing Kalb-Ramond gravity with charged rotating black holes: constraints from EHT observations Nengroo, Towheed Ahmad Islam, Shafqat Ul Ghosh, Sushant G. General Relativity and Quantum Cosmology The Event Horizon Telescope (EHT) has guided strong-field gravitational physics by providing the first direct images of the supermassive black holes M87* and Sagittarius A*. The EHT observations offer unprecedented opportunities to test modified gravity theories against general relativity (GR). Motivated by this, we investigate charged rotating black holes in KR gravity, a framework motivated by string theory that incorporates spontaneous Lorentz symmetry breaking. The spacetime geometry is characterized by a Lorentz--violating parameter $\ell$ and electric charge $Q$, which modify the Kerr--Newman metric through a radial-dependent mass function. We compute black hole shadows and derive constraints on $\ell$ and $Q$ using EHT observations of M87* and Sgr A*. For angular shadow diameter $θ_{\rm sh}$ of M87* at inclination $θ_o=17^\circ$ and fixed $Q=0.2$, the EHT-allowed range $θ_{\rm sh}\in(35.1,\,40.5)\,μ\mathrm{as}$ constrains the Lorentz--violating parameter to approximately $-0.019\lesssim\ell\lesssim0.075$ and $-0.076\lesssim\ell\lesssim0.029$ across the admissible spin interval. For angular shadow diameter $θ_{\rm sh}$ of Sgr A* at inclination $θ_o=50^\circ$ and fixed $Q=0.2$, the corresponding EHT-allowed range $θ_{\rm sh}\in(41.7,\,55.7)\,μ\mathrm{as}$ permits approximately $-0.075\lesssim\ell\lesssim0.110$ and $-0.124\lesssim\ell\lesssim0.076$ across the admissible spin interval. Our analysis reveals that the Lorentz-violating parameter suppresses the shadow radius by a factor $\sqrt{1-\ell}$, while charge introduces additional distortions. Using the angular shadow diameter measured by EHT, we obtain an upper bound $\ell \lesssim 0.19$ from Sgr A* data with the stellar dynamics mass prior. |
| title | Probing Kalb-Ramond gravity with charged rotating black holes: constraints from EHT observations |
| topic | General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2604.13494 |